bpo-28254: Add a C-API for controlling the GC state (GH-25687)

Add new C-API functions to control the state of the garbage collector:
PyGC_Enable(), PyGC_Disable(), PyGC_IsEnabled(),
corresponding to the functions in the gc module.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Doc/c-api/gcsupport.rst

@@ -173,3 +173,46 @@ if the object is immutable.
    this method (don't just call :c:func:`Py_DECREF` on a reference).  The
    collector will call this method if it detects that this object is involved
    in a reference cycle.
+
+
+Controlling the Garbage Collector State
+---------------------------------------
+
+The C-API provides the following functions for controlling
+garbage collection runs.
+
+.. c:function:: Py_ssize_t PyGC_Collect(void)
+
+   Perform a full garbage collection, if the garbage collector is enabled.
+   (Note that :func:`gc.collect` runs it unconditionally.)
+
+   Returns the number of collected + unreachable objects which cannot
+   be collected.
+   If the garbage collector is disabled or already collecting,
+   returns ``0`` immediately.
+   Errors during garbage collection are passed to :data:`sys.unraisablehook`.
+   This function does not raise exceptions.
+
+
+.. c:function:: int PyGC_Enable(void)
+
+   Enable the garbage collector: similar to :func:`gc.enable`.
+   Returns the previous state, 0 for disabled and 1 for enabled.
+
+   .. versionadded:: 3.10
+
+
+.. c:function:: int PyGC_Disable(void)
+
+   Disable the garbage collector: similar to :func:`gc.disable`.
+   Returns the previous state, 0 for disabled and 1 for enabled.
+
+   .. versionadded:: 3.10
+
+
+.. c:function:: int PyGC_IsEnabled(void)
+
+   Query the state of the garbage collector: similar to :func:`gc.isenabled`.
+   Returns the current state, 0 for disabled and 1 for enabled.
+
+   .. versionadded:: 3.10